The present invention relates generally to machines for applying a liquid, such as glue or other liquid substances, to a moving web, and more particularly to a novel method and apparatus for preventing slinging of liquid from high speed rotating rolls within a liquid applicator machine or the like.
It is a conventional practice in the art of web printing presses and the like, to pass a web of material, such as paper, through a machine operative to selectively apply a liquid glue and/or other liquid substances to the web as it is passed through the liquid applying machine from, for example, a printing press. Such machines, typically termed pattern gluers, generally employ a plurality of cooperating cylindrical rollers to transfer liquid from a liquid source to the moving web, the rolls or cylinders conventionally including a pan roller, a transfer roll or cylinder, a plate cylinder and an impression cylinder. The rolls and cylinders are generally supported for rotation about horizontal axes, with the pan roller being partially submerged within a liquid reservoir and rotated at a relatively low speed so as to transfer liquid from the reservoir to the transfer roll which is rotated at a relatively high speed matching the surface speed of the web material passing through the liquid applicator machine. The pan and transfer rolls are maintained in predetermined spatial and rotational speed relation such that the liquid carried on the pan roll creates a metered liquid layer or film on the transfer roll. The liquid layer or film formed on the transfer roll is then transferred to an exposed pattern surface of a closed cell rubber pad carried on the rotating plate cylinder so as to selectively apply the liquid to the moving web of paper material. A fourth roll or cylinder, generally termed the impression cylinder, is located on the opposite side of the moving web from the plate cylinder and serves to maintain the moving web material stable against the plate cylinder and thereby assist in transferring the liquid film from the pattern pad on the plate cylinder to the moving web material. Such liquid applicator machines are of generally two types, one of which is operative to apply a patterned glue or other liquid substances to the lower surface of a moving web material passing through the machine and the other of which is operative to apply glue or other liquid substances to the upper surface of the web material.
A significant problem which exists with known liquid applicator machines, and particularly applicator machines of the aforementioned type employing a relatively low speed pan roll and a relatively high speed transfer roll cooperative to effect transfer of a metered layer of liquid from the pan roll to the transfer roll, is that the liquid picked up by both the outer cylindrical surface and end surfaces of the pan roll from the liquid reservoir is generally transferred to the transfer roll in a manner which causes liquid accumulation at the opposite end edges and corresponding end surfaces of the transfer roll from which the accumulated liquid is slung off. Such slinging of liquid from the transfer roll may necessitate slow-down of the machine as well as cause damage to the moving web material with resulting potential for breakage. This problem has been particularly acute where the pan roll has a shorter length than the transfer roll such that liquid carried upwardly to the transfer roll by the end surfaces of the pan roll tends to be deposited onto the adjacent outer peripheral surface areas of the transfer roll and migrate to the corresponding outer end edges and around onto the associated end surfaces of the transfer roll from which the liquid is slung off by the inertia of high-speed rotation. A similar problem exists where the pan roll is of substantially the same length as the transfer roll in that liquid carried upwardly on the end surfaces of the pan roll is generally transferred directly onto the corresponding end surfaces of the transfer roll from which the liquid is slung outwardly by the centrifugal forces created by high-speed rotation of the transfer roll.
One attempt to eliminate the aforedescribed problem of liquid slinging within liquid applicator machines includes positioning a stationary scraper or wiper type device adjacent each of the opposite end edges of the transfer roll so as to scrape off the accumulated liquid transferred onto the transfer roll from the pan roll. This technique is of limited value in that many viscous liquids, such as glue and the like, accumulate to a point where continued build-up of liquid on the scraper blades causes the liquid to climb over the scraper blades onto the corresponding outer end surfaces of the high speed transfer roll from which the liquid is flung outwardly to thereby create the very problem the scraper or wiper blades were intended to cure. In either event, the scraper or wiper blades must be continually removed and cleaned, thereby necessitating down time of the machine with attendant increased maintenance costs.
Similar problems exist in liquid applicators of the type adapted to apply a plurality of different liquids to a moving web. Such machines, generally termed segmented applicators, employ a transfer roll having a plurality of axially spaced discreet cylindrical segments each of which cooperates with an associated pan roll and liquid reservoir to effect transfer of liquid from the reservoir to the corresponding transfer roll segment from which the liquid is transferred to the moving web material through a plate cylinder in a conventional manner. The problem of liquid slinging from the opposite ends of the various transfer roll segments is particularly troublesome in this type of liquid applicator machine because the slung liquid droplets cause contamination by intermixing with the different liquids in other liquid reservoirs. Thus, significant problems exist in the known liquid applicator machines as a result of liquid slinging from the high speed transfer rolls. The present invention addresses these problems.